Through a friend of his ex-wife, O'Brien got a gig writing Episode 37 of the animated series Rugrats, "Toys in the Attic", which premiered in 1992 under his only known pseudonym, Carroll Mine. According to his sister, Erin, he was disgusted with editorial changes made to his script.[1]

O'Brien committed suicide by gunshot two weeks after learning that his novel, Leaving Las Vegas, was to be made into a movie. His father says that the novel was his suicide note. Two more of his novels were published posthumously: Stripper Lessons (Grove Press, 1997) and The Assault on Tony's (Grove Press, 1996), both of which had been left unfinished at the time of his death and were completed by his sister, Erin.[1] A third manuscript, Better, was published by Akashic Press in 2009.